The present invention relates to an improved, tinted tape cassette which allows an optical tape end sensing mechanism installed in an audio or video tape recording and playback apparatus to accurately sense an end of a magnetic tape without malfunctions.
A magnetic tape housed in a commerically available audio or video tape cassette is usually headed and tailed by clear strips. As well known in the art, as soon as a photosensor senses such a clear tape portion while the tape in the cassette is transported for recording or playback, the tape transport is interrupted. The photosensor is built in an audio or video recording and playback apparatus and customarily comprises a light emitting element and light receiving elements. These light emitting elements are so located that a light path between them is crossing the tape stretched along a tape path inside the cassette when the cassette is loaded in the apparatus. While the light receiving element is customarily located at each side of the cassette. Each light receiving element, upon sensing light issuing from the light emitting element and transmitted through a clear strip at a tape end, detects that an end of the tape has been reached, thereby causing the tape transport to be stopped. The problem encountered with this type of arrangement is occasional failures of tape end detection attributed to an unintended light reaching the light receiving element, for various reasons which causes an interruption of the tape transport and, thereby, disturbs the desired recording or playback operation.
Various kinds of light are possibly incident to either or both of the light receiving elements mentioned above. One of them is, of course, the intended light issued from the light emitting element and transmitted through clear strips of the magnetic tape. The others are such an ambient light incident to the outer surfaces of a tape cassette and scattered thereby to the interior of the recording and playback apparatus than a part of them reaching to the light receiving element, the light incident to the tape cassette to propagate through the material constituting the cassette and, then, partly coming out of the cassette to reach the light receiving element, the light entering the tape cassette through transparent windows of the cassette, diffused within the cassette and, then, partly directed out of the cassette toward the light receiving element, etc. Should the light receiving element sense such undesired kinds of light, the tape end sensing mechanism would be actuated falsely to cause abrupt stop of tape transport despite the fact than an end of a magnetic tape is not reached.
Prevention of such malfunctions of the tape end sensing mechanism has heretofore been implemented by mixing carbon black with the material of a tape cassette to color it black so that undesired light may be prevented from entering the cassette or being reflected by outer surfaces of the cassette. The result has been a production of tape cassettes limited in black only, which are drab and far from aesthetic sensations. Where it is desired to color tape cassettes in variations such as in blue, green, brown, yellow-brown or the like for marketing reasons, the desired color is unattainable unless the amount of carbon black to be mixed with the material of the tape cassettes is reduced to zero or, if not to zero, to a significantly small value in the event of mixing a pigment or the like of that color into the material. Therefore, simply adapting a desired color to tape cassettes without considering the optical sensing mechanism would result in malfunctions of the mechanism. Due to such problemmatic situation, tape cassettes for use with a recording and playback apparatus having a tape end sensing mechanism have been colored black or almost black without exception, despite the demand for colorful tape cassettes.